Old English aldormonn (Mercian), ealdormann (West Saxon) "ruler, prince, chief; chief officer of a shire," from aldor, ealder "patriarch" (comparative of ald "old;" see old) + monn, mann "man" (see man (n.)). A relic of the days when the elders were automatically in charge of the clan or tribe, but already in Old English used for king's viceroys, regardless of age. The word yielded in Old English to eorl, and after the Norman Conquest to count (n.). Meaning "headman of a guild" (early 12c.) passed to "magistrate of a city" (c.1200) as the guilds became identified with municipal government.

A member of a city council. Aldermen usually represent city districts, called wards, and work with the mayor to run the city government. Jockeying among aldermen for political influence is often associated with machine politics.